A number of food extrusion processes require an equal flow of material from a number of dies which are fed from the same die holder. If the flow of material is unequal then the resulting product streams are also non-uniform which is undesirable. This is particularly true if the food material is cut to a predetermined length with an estimated weight for packaging based upon the length, which is not unusual in extruded food packaging.
A number of arrangements have been provided to attempt to provide equal amounts of food material from a number of dies with each die extruding the same quantity per unit time. Previous attempts have been directed to producing the same pressure on each die in an attempt to obtain the same quantity of extruded product per unit time.
A example of the prior art, before an attempt was made to obtain equal pressure on each die, is shown in FIG. 1. Here extrusion apparatus 12 has a source of heated material introduced through pipe 32 into a manifold 26, which can be heated. Dies 18 are all connected to die holder 20, which has a conduit 21 opposite each die from die holder 20 into manifold 26. The result of this arrangement is shown in FIG. 1A with the resulting pressure in pounds per square inch (PSI) as a function of die location 13. FIG. 1A is also positioned opposite FIG. 1 such that the die locations of FIG. 1A all directly relate to the die 18 locations of FIG. 1. Since pipe 32 is centrally located the maximum pressure is also centrally located with a reduction in this pressure outwardly in both directions as shown in FIG. 1A.
An attempt to remedy this situation is shown in FIG. 2 where extrusion apparatus 14 has two pipes 34 feeding heated pressurized food material into manifold 28. Conduits 23 extend between manifold 28 to die holder 22 opposite each die 18. The results of this arrangement is shown in FIG. 2A with the resulting pressure in pounds per square inch (PSI) plotted as a function of die location 15. FIG. 2A is also positioned opposite FIG. 2 such that die 18 locations of FIG. 2A correspond to the die locations of FIG. 2. Since pipes 34 are spaced approximately one-third of the distance along manifold 28, two maximums essentially opposite pipes 34 occur, with a reduction in these pressures outwardly in both directions as shown in FIG. 2A. This is an improvement over the results of extrusion apparatus 12 but the pressure of each die is still far from equal.
An improved attempt to provide equal pressure on dies 18 is shown in FIG. 3 with extrusion apparatus 16 again having only one pipe 36 feeding heated pressurized food material into manifold 30. Conduits 25 extend between manifold 30 to die holder 24 opposite each die 18. Here however each die 18 has a valve 38 in connection 23 to die holder 24. Valves 38 permit adjusting the pressure on each die 18 independently. The results of this arrangement is shown in FIG. 3A with the resulting pressure in pounds per square inch (PSI) plotted as a function of die location 17. FIG. 3A is also positioned opposite FIG. 3 such that die 18 locations of FIG. 3A correspond to the die locations of FIG. 3. Here the resulting pressure is nearly equal at all dies because valves 38 have been adjusted to achieve this result.
Even extrusion apparatus 16 does not produce the desired result of a uniform quantity of material extruded from each die 18 over any given time period. This results because the quantity being adjusted, namely pressure, is not the quantity which must be kept uniform, namely extruded material per unit time. Equal pressure on dies 18 will only produce equal flow if the material friction to and through each die remains identical, and if the material being extruded through each die has identical viscosities. Any difference in the temperature of a food material will result in a change in its viscosity, with lower temperatures resulting in greater viscosity. Dies 18 located at the ends of die holder 24 will receive material which has a longer flow path with a greater length of time to cool with a resulting greater viscosity, which will cause some of to adhere to the die intake reducing its size and increasing its friction. While a small differential is insignificant initially, the effects build up exponentially with time. Consequently, a small reduction in flow caused by lower temperature causing greater viscosity will result in the material being fed to that die flowing even slower, which increases the temperature differential even further. This builds up into a catastrophic failure quickly until the die is blocked completely. This is an inevitable result of any temperature differential in the material, and will always result in die blockage. Once even one die is blocked the die assembly must be disassembled and cleaned before it can be used further. These problems are multiplied when extruding multiple phases at one time, or when the material contains lumps of material of a size which can plug a die. Meisner, in U.S. Pat. Nos. 4,925,380 and 5,019,404 utilizes a scheme for manufacturing a multicolored aerated confection product utilizing multi-orifice extrusion system for extruding multiple strands of a confection material. These apparatus have the problems discussed above since no provision is made for metering equal amounts of material through individual dies.
A number of apparatus utilize positive displacement metering of both plastic and food materials to extrusion apparatus obtain a uniform product. These include Fox, U.S. Pat. No. 4,336,213; Rahlfs, U.S. Pat. No. 4,171,193; Fritsch, U.S. Pat. No. 3,649,147; R. Levison et al., U.S. Pat. No. 3,078,513; H. Corbett, U.S. Pat. No. 2,680,880; and Marin, U.S. Pat. No. 5,182,066
All of these positive displacement metering apparatus drive only a single extrusion die. There is no teaching of using a number of synchronized positive metering apparatus to provide a plurality of uniform and equal extrusions.
This invention positively meters food material through a plurality of dies. This assures that all flows remain open to all dies and rate predetermined by the capacity of the various metering means. This result is obtained regardless of the temperature of the material flow to any given die and completely overcomes the problems of all previous extrusion apparatus to multiple dies, where even a small temperature differential will always cause the catastrophic failure of total die blockages.
In the prior art using pressure balancing to obtain uniform flow through multiple dies, the flow rates are dependent upon the sum of all pressure losses along all flow paths including the flow path through each die. This invention frees the die designer from the constraint of balancing the pressure losses in each flow path to the individual dies. This can greatly simplify the die design itself, which results in a die easier to manufacture and clean. As an alternative, a more complex die can now be used to obtain previously unattainable results.